I worked hand-in-hand with Pettit Paint Support Manager, Margo Hunt, in developing this story. It appears in the April, 2016 issue of Boating Magazine as one part of an article titled, How To Prep Your Boat For Bottom Paint. Osmotic blistering on older (and sometimes relatively new) hulls and those previously bottom painted is a major concern, so much so that Pettit created a bulletin describing how to deal with it.
Here are two approaches to ensuring good adhesion with no blistering:
High Build Epoxy Primer Method
Pettit recommends this method where hull blistering has been a problem; also on boats that have had their finish stripped by soda or sandblasting. This primer is a heavy duty two-part epoxy coating. It reduces the chance of fiberglass water absorption so it's excellent at preventing hull blisters. It's highly recommended for maximum durability in salt water.
•Clean and de-wax the hull as noted in the steps above using 92 Bio-Blue Hull Surface Prep, D-95 Dewaxer, or 120 Brushing Thinner.
•Apply at least three coats of Pettit Protect Hi-Build Epoxy Primer. Total dry film thickness is more important than the number of coats. Twelve (12) mils thickness is recommended for metal and fiberglass hulls.
•Finish with two coats of Pettit antifouling bottom paint.